Ceramic arc tube mounting structure

ABSTRACT

An improved mounting structure in a high intensity discharge lamp accommodating thermal expansion of a ceramic arc tube mounted on a support frame within an outer vitreous envelope. One end of the arc tube is rigidly fastened to the frame, while the other end is secured by an axial lead wire which extends from a ceramic plug through a single close-fitting loop in a transverse support wire and a flexible conductor provides the electrical connection. Close fitting round wires are used for the axial lead and the transverse support, permitting one to slide within the other without seizing or binding and without rattling.

United States Patent 11 1 1111 3,882,346 McVey 1 May 6, 1973 1 CERAMIC ARC TUBE MOUNTING 3,623,134 11 1971 Werner 313 25 STRUCTURE 3,746,914 7/1973 Olson et al 313/17 [75] Inventor: Charles I. McVey, Shaker Heights,

Ohio

[73] Assignee: General Electric Company,

Schenectady, NY.

[22] Filed: Nov. 5, 1973 [21] Appl. No.: 412,659

[52] US. Cl. 313/253; 313/18; 313/25; 313/184 [51] Int. Cl H01j 1/88; H01] 19/42 [58] Field of Search 313/17, 18, 25, 184, 253

[56] References Cited UNITED STATES PATENTS 2,272,467 2/1942 Kern et al. 313/25 X 3,333,132 7/1967 Edris et al 313/17 3,558,963 l/197l Hanneman et a1 313/184 Primary ExaminerSaxfield Chatmon, Jr. Attorney, Agent, or Firm-Ernest W. Legree; Lawrence R. Kempton; Frank L. Neuhauser [57 ABSTRACT v An improved mounting structure in a high intensity discharge lamp accommodating thermal expansion of 10 Claims, 3 Drawing Figures CERAMIC ARC TUBE MOUNTING STRUCTURE BACKGROUND OF THE INVENTION The invention relates to a high intensity discharge lamp comprising a ceramic are tube mounted within an outer glass envelope or jacket.

Crystalline alumina ceramic has a coefficient of linear expansion of 8 X per C and the arc tube of this material in a high pressure sodium vapor lamp may be heated in operation to an average temperature of 1000C or higher. In a typical 400-watt lamp, the arc tube which is 1 10 millimeters long will expand about 1 millimeter. The metal support frame and the vitreous outer envelope will not expand nearly as much, and the expansion of the various parts does not occur at the same time when the lamp is warming or cooling. Where metal end caps are used to seal the ends of the alumina tube and a single side rod frame extending substantially the length of the outer envelope is used to mount the arc tube, the use of relatively flexible strapping between the end caps and the frame plus the resiliency of the end caps and the natural springiness of the frame is generally adequate to accommodate any differential expansion between the ceramic arc tube and the mounting frame.

In a new design of alumina ceramic arc tube, one of the metal end caps is replaced by a ceramic plug having a central perforation through which a slender inlead wire is sealed. With this construction, the mounting arrangements which were formerly adequate cause excessive fatigue of the inlead wire into the ceramic plug, resulting in premature failure.

In some alumina ceramic lamps utilizing alumina end plugs, a tubular inlead has been sealed into the plug and a pin-like supporting member arranged to slide in the tubular inlead. An example of this construction is shown in US. Pat. No. 3,609,437 Tol et al., issued September, 1971. I have found that even when this construction is reversed by attaching the wire to the ceramic plug and the tube to the metal frame, it is not entirely satisfactory. Unless there is appreciable clearance for the wire within the tube, seizing or binding may occur if the parts are not perfectly straight or if parts are used having sharp edges. On the other hand with adequate clearance, the excessive play tends to bend the inlead wire when the lamp is jarred or mishandled. Also the lamp tends to rattle when shaken and such a lamp may sing or hum in its fixture in operation. This detracts from its value.

SUMMARY OF THE INVENTION The object of the invention is to provide a simple and inexpensive ceramic arc tube mounting structure accommodating thermal expansion and overcoming the foregoing problems.

In accordance with my invention, the lower end of the arc tube which is normally provided with a metal end cap is rigidly attached to the frame. The upper end is sealed by a ceramic plug through which extends a relatively slender axial wire lead. This wire lead is extended through a single close-fitting loop in a transverse support wire, and a flexible conductor joins the wire lead to the frame to provide the electrical connection. Both the axial wire lead and the transverse sup port wire are round wire with the transverse support wire making a close fit in a single loop around the axial lead wire. This permits the axial lead wire to slide within the transverse support wire without seizing or binding and without rattling when the lamp is shaken. Preferably the flexible conductor is a metal ribbon which is stressed in order to bias the wire lead against one side of the loop and damp any sonic vibrations.

DESCRIPTION OF DRAWING FIG. 1 is a side elevation view of a ceramic arc tube lamp embodying the present invention.

FIG. 2 is a fragmentary pictorial view to a larger scale of the upper portion of the arc tube mount of FIG. 1.

FIG. 3 is a fragmentary pictorial view to a larger scale of the upper portion of the mount in a lamp intended for base-up operation.

DETAILED DESCRIPTION Referring to the drawing wherein like reference characters represent similar parts throughout the several views, there is illustrated in FIG. 1 a discharge lamp 1 having a ceramic arc tube mounting structure embodying the invention. The lamp comprises an outer envelope of glass 2 attached to a standard mogul screw base 3, and comprising a re-entrant stem press 4 through which extend, in conventional manner, a pair of relatively heavy lead-in conductors 5, 6 whose outer ends are connected to the screw shell 7 and eyelet 8 of the base.

The arc tube 9 centrally located within the outer envelope comprises a piece of crystalline alumina tubing having its lower end closed by a metal end cap 10, suitably of niobium which matches the expansion coefficient of alumina ceramic. A metal tube 11 which may also be of niobium is hermetically sealed through the cap and serves as an exhaust and fill tubulation during manufacture of the lamp. The exhaust tube is sealed off at its outer end and serves as a reservoir in which excess sodium-mercury amalgam condenses during operation of the lamp. The lower electrode within the lamp is attached to the inward projection of tube 11. A relatively short rigid wire connector 12 is welded to tube 11 and to short support rod 13 which, in turn, is welded to inlead conductor 5. Support rod 13 is braced to single side rod 14 and lead-in conductor 6 by means of a strap 15 attached to it and wrapping around an insulator l6 threaded over support rod 13. Thus the lower end of arc tube 9 is quite rigidly fixed in place and provision for thermal expansion must be made at the upper end.

The upper end of the arc tube is sealed by an alumina ceramic plug 17 best seen in FIG. 2. The plug is centrally perforated and a slender niobium inlead wire 18 is sealed through the hole and has the upper electrode attached to its projection within the arc tube. The various seals including that of the ceramic plug to the arc tube and that of the inlead wire through the ceramic plug may be made using various sealing compositions, sometimes referred to as sealing glass, which comprise primarily aluminum oxide and.calcium oxide. 1 have successfully used the composition designated G54 consisting by weight of approximately 54.0% AI O 38.5% CaO, and 7.5% MgO. Other compositions which may be used are those described in US. Pat. No. 3,281,309 Ross, US. Pat. No. 3,441,421 Sarver et al., and my own US. Pat. No. 3,588,577. By way of example, with the G-54 sealing composition the seals are made at a temperature of about 1500C in a vacuum. The molten glassy seal material wets and flows by capillary action into the close space between the ceramic end plug and the tube wall and around the lead wire 18 where it passes through the aperture in the plug. The interstices are filled with the sealing material and the angles between the faying surfaces are filleted with the material as indicated at 19. The bowed wire cross piece 20 spot-welded to inlead l8 rests against the upper end of ceramic tube 9 and supports the inlead, electrode and ceramic plug assembly during the sealing operation.

The ceramic arc tube is maintained in the center of the outer envelope which is evacuated by pumping and then flashing the getter rings 21. The are tube is supported by a metal frame comprising side rod 14 which extends from inlead 6 up to dimple 22 at the dome end which it engages by means of a resilient clamp 23. The side rod is extended beyond the clamp into a downwardly reverted portion 24 which passes on the other side of lead wire 18. A transverse support wire 25 extends from side rod 14 across to portion 24 and makes a single close-fitting loop 26 around slender inlead 18. A curved resilient metal ribbon 27 provides the necessary electrical connection between side wire 14 and inlead 18.

Both inlead 18 and transverse support 25 are round or circular cross-section wires and the loop in member 25 is accurately sized to accommodate inlead 18 with slight clearance. The use of close-fitting adjoining curved surfaces permits the inlead wire to slide within the loop without seizing or binding. The arrangement permits reducing the clearance to the point where substantially no sound is created when the lamp is bumped or shaken. At the same time the flexible resilient metal ribbon 27 provides damping of any vibrations by biasing the inlead against one side of the loop. The mechanical resiliency of the system is provided in part by curved metal ribbon 27, in part by the transverse support member 25 and inlead 18 which are relatively flexible, and in part by the supporting frame including side rod 14 which is itself flexible. There is thus provided a flexible mounting which permits thermal expansion of the arc tube without exerting any strain on the seals or inleads or causing any permanent thermal set of the mounting frame 14.

The close fit of the parts avoids excessive play which tends to bend the inlead wire should the lamp be jarred or mishandled. Finally the construction eliminates undesirable rattling when the lamp is shaken or subjected to vibration, and singing or humming when the lamp is operated.

Lead wire 18 is preferably made of niobium which matches the expansion coefficient of alumina ceramic. The lead wire operates at about 700C, and transverse support wire 25 varies from about 700C at the contact point with the lead wire, to about 450C at the attachment to the frame. Flexible ribbon connector 27 varies from about 650C at the inlead to about 450C at the frame. In order to prevent recrystallization of these parts at these relatively high operating temperatures over the life of the lamp, a refractory metal such as niobium is preferred, though zirconium, titanium, vanadium, molybdenum, tantalum, tungsten and alloys thereof can also be used. When parts made of these metals need to be formed from flat stock by slitting and precision stamping, they are relatively expensive. My invention avoids this expense by using only wire for transverse support 25, and a ribbon which may be made by rolling wire flat for flexible connector 27. By way of example, in a 400 watt lamp for base down operation, inlead 18 was Nb 1% Zr wire 0.9 mm in diameter, transverse support 25 was Nb 1% Zr wire 0.5 mm in diameter, and flexible connector 27 was Nb 1% Zr wire 1.1 mm in diameter flattened to 0.15 mm thickness by 2.4 mm width.

The lamp illustrated in FIGS. 1 and 2 is intended for base down operation and has the niobium exhaust tube 11 arranged to be located lowermost when the lamp is installed in the fixture. FIG. 3 illustrates a variant of the invention wherein the exhaust tube is reversed end for end relative to the outer envelope so that the metal exhaust tube again is located lowermost when the lamp is installed. The fragmentary view shows the stem press 4 and the upper end of arc tube 9. The getter rings 21 and the bowed cross piece 20 have been eliminated from the figure. The lower end of the arc tube having the metal cap and exhaust tube is then connected by means of a welded wire connector to the single side rod 14 at the dome end of the lamp. The upper end of the arc tube is supported by and connected to support rod 13 by means of a transverse support wire 28 welded to rod 13 at one end and having a single loop 29 at its distal end which encircles inlead 18 making a close fit with it but allowing some clearance for axial movement. Curved resilient metal ribbon 27, as before, provides the necessary electrical connection and serves as a vibration damper.

To assure approximately the same resiliency with this variant as in the construction of FIGS. 1 and 2, transverse support wire 28 which is attached at one end only, is made heavier than transverse support wire 25 in FIGS. 1 and 2 which is attached at both ends. For a base up lamp corresponding to the base down example previously given, transverse support number 28 was Nb 1% Zr wire 0.9 mm in diameter. In order to have the desired resilience and also for reasons of economy, transverse support niobium wires 25 or 28 are no greater in diameter than niobium lead wire 18, and wire 28 is preferably appreciably smaller.

In tests of lamps using high purity nickel and iron wires for members 25, 27 and 28, these less refractory metals have been found unsatisfactory for the application due to excessive vaporization or excessive grain growth at the operating temperature in lamps rated for 20,000 hour lives.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high intensity discharge lamp comprising:

an outer vitreous envelope domed at one end and having a base attached to the other end, and a pair of inleads sealed into said envelope and connected to said base;

a tubular ceramic envelope having electrodes sealed therein and containing an ionizable medium, a closure at the lower end of said envelope including a metal member serving as an inlead to the electrode, and a closure at the upper end of said envelope comprising a ceramic plug and a slender lead wire sealed therethrough;

an arc tube mounting frame within said envelope comprising one side rod extending from one inlead to the dome end of said envelope, and a short support rod extending from the other inlead, said metal member inlead being rigidly connected to one of said rods;

a transverse support member extending across from the other of said rods, said transverse support member being a smooth round wire making a single close-fitting loop around said slender lead wire, and a flexible conductor connecting said slender 5 lead wire to said other rod.

2. A lamp as in claim 1 wherein said flexible conductor is a resilient metal ribbon.

3. A lamp as in claim 1 wherein said transverse support wire is smooth round wire of metal from the group consisting of niobium, zirconium, titanium, vanadium,

molybdenum, tantalum, tungsten and alloys thereof.

4. A lamp as in claim 3 wherein said flexible conductor is a resilient ribbon of metal from the group consisting of niobium, zirconium, titanium, vanadium, molybdenum, tantalum, tungsten and alloys thereof.

5. A lamp as in claim 1 wherein said slender lead wire and said transverse support wire are both smooth round niobium wire.

6. A high intensity discharge lamp comprising:

an outer vitreous envelope domed at one end and having a base attached to the other end, and a pair of inleads sealed into said envelope and connected to said base;

a tubular ceramic envelope having electrodes sealed therein and containing an ionizable medium, a niobium metal end cap closure at 'the lower end of said envelope including a metal tube projecting through said end cap and serving as an inlead to the electrode, and a closure at the upper end of said envelope comprising a disc-like ceramic plug having a central perforation and a slender niobium lead wire sealed therethrough;

an arc tube mounting frame within said envelope comprising one side rod extending from one inlead to the dome end of said envelope, and a short support rod extending from the other inlead, said metal tube inlead being rigidly connected to one of said rods;

a transverse support member extending across from the other of said rods, said transverse support member being a smooth round refractory metal wire making a single close-fitting loop around said slender lead wire, and a curved resilient metal ribbon connecting said slender lead wire to said other rod and serving to bias said slender lead wire against one side of said loop.

7. A lamp as in claim 6 for base down operation wherein said metal tube inlead is rigidly connected to said short support rod, said side rod extending to the dome end of said envelope includes a reverted portion passing on the other side of said slender lead wire, and said transverse wire support member making a single loop around said slender lead wire extends from said side rod to said reverted portion.

8. A lamp as in claim 6 for base up operation wherein said metal tube inlead is rigidly connected to said side rod extending to the dome end of said envelope, and said transverse wire support member extends from said short support rod and makes a single close-fitting loop at its distal end around said slender lead wire.

9. A lamp as in claim 6 wherein said transverse wire support member is no greater in diameter than said slender lead wire and is of metal from the group consisting of niobium, zirconium, titanium, vanadium, molybdenum, tantalum, tungsten and alloys thereof.

10. A lamp as in claim 9 wherein said curved resilient ribbon is of metal from the group consisting of niobium, zirconium, titanium, vanadium, molybdenum,

tantalum, tungsten and alloys thereof.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTWN PATENT NO. 3,

DATED I May 6, 1973 INVENTOR(S) Charles I. McVey it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On page 1 in the heading "May 6, 1973 should read May 6, 1975-- gignccl and gealcd this twenty-sixth D3) 0f August 1975 [SEAL] AIIGSI.

RUTH c. MASON c. MARSHALL DANN Alls l'ng ()ffi (mnmissimwr uj'PatenIs and Trademarks 

1. A high intensity discharge lamp comprising: an outer vitreous envelope domed at one end and having a base attached to the other end, and a pair of inleads sealed into said envelope and connected to said base; a tubular ceramic envelope having electrodes sealed therein and containing an ionizable medium, a closure at the lower end of said envelope including a metal member serving as an inlead to the electrode, and a closure at the upper end of said envelope comprising a ceramic plug and a slender lead wire sealed therethrough; an arc tube mounting frame within said envelope comprising one side rod extending from one inlead to the dome end of said envelope, and a short support rod extending from the other inlead, said metal member inlead being rigidly connected to one of said rods; a transverse support member extending across from the other of said rods, said transverse support member being a smooth round wire making a single close-fitting loop around said slender lead wire, and a flexible conductor connecting said slender lead wire to said other rod.
 2. A lamp as in claim 1 wherein said flexible conductor is a resilient metal ribbon.
 3. A lamp as in claim 1 wherein said transverse support wire is smooth round wire of metal from the group consisting of niobium, zirconium, titanium, vanadium, molybdenum, tantalum, tungsten and alloys thereof.
 4. A lamp as in claim 3 wherein said flexible conductor is a resilient ribbon of metal from the group consisting of niobium, zirconium, titanium, vanadium, molybdenum, tantalum, tungsten and alloys thereof.
 5. A lamp as in claim 1 wherein said slender lead wire and said transverse support wire are both smooth round niobium wire.
 6. A high intensity discharge lamp comprising: an outer vitreous envelope domed at one end and having a base attacHed to the other end, and a pair of inleads sealed into said envelope and connected to said base; a tubular ceramic envelope having electrodes sealed therein and containing an ionizable medium, a niobium metal end cap closure at the lower end of said envelope including a metal tube projecting through said end cap and serving as an inlead to the electrode, and a closure at the upper end of said envelope comprising a disc-like ceramic plug having a central perforation and a slender niobium lead wire sealed therethrough; an arc tube mounting frame within said envelope comprising one side rod extending from one inlead to the dome end of said envelope, and a short support rod extending from the other inlead, said metal tube inlead being rigidly connected to one of said rods; a transverse support member extending across from the other of said rods, said transverse support member being a smooth round refractory metal wire making a single close-fitting loop around said slender lead wire, and a curved resilient metal ribbon connecting said slender lead wire to said other rod and serving to bias said slender lead wire against one side of said loop.
 7. A lamp as in claim 6 for base down operation wherein said metal tube inlead is rigidly connected to said short support rod, said side rod extending to the dome end of said envelope includes a reverted portion passing on the other side of said slender lead wire, and said transverse wire support member making a single loop around said slender lead wire extends from said side rod to said reverted portion.
 8. A lamp as in claim 6 for base up operation wherein said metal tube inlead is rigidly connected to said side rod extending to the dome end of said envelope, and said transverse wire support member extends from said short support rod and makes a single close-fitting loop at its distal end around said slender lead wire.
 9. A lamp as in claim 6 wherein said transverse wire support member is no greater in diameter than said slender lead wire and is of metal from the group consisting of niobium, zirconium, titanium, vanadium, molybdenum, tantalum, tungsten and alloys thereof.
 10. A lamp as in claim 9 wherein said curved resilient ribbon is of metal from the group consisting of niobium, zirconium, titanium, vanadium, molybdenum, tantalum, tungsten and alloys thereof. 